Switching transistors are frequently used in automotive control systems in which the emitter-collector path of a switching transistor is serially connected with the primary of an ignition coil. To store electromagnetic energy in the coil, the emitter-collector path is controlled to become conductive, thus permitting current to flow from a vehicle battery through the primary of the ignition coil. Upon control of the transistor to blocked or OFF condition, the current is interrupted abruptly causing, by transformer action, release of the stored electromagnetic energy to the secondary of the ignition coil and flash-over of a spark plug. The transistor has to be controlled to conduction or to blocked state by a driver circuit which, in turn, is controlled by a control signal source coupled to the crankshaft of the engine, directly or through a microprocessor, for example, so that current flow through the switching transistor is appropriately controlled, and the switching transistor is gated OFF at the proper instant of time for generation of a spark in accordance with a predetermined crankshaft position of the engine.
The ignition switching transistor, itself, is controlled to conduction or non-conduction by a control circuit which includes driver transistors for the switching transistor, see, for example, German Patent Disclosure Document DE-OS No. 19 01 557.